In the field of sawmill operation it is necessary, as one of the steps for preparing a log, the bark of the log is separated from the log. While the technology appears to draw from the field of wood chippers and adzes, it is distinct in that while it is necessary to remove the bark by abrading, it is deleterious to the log to cut significantly into the wood. Thus a cutting head or adz which is equally adapted to chipping wood as well as bark is unsatisfactory for the use.
Two major forms of debarkers are in common use. Typically each depends upon the fact that the shear strength of the bark is weakest in the cambium layer between the wood and the bark.
Once such form of machine is known as the hollow rotor type in which a plurality of arms, swing mounted to a rotary collar extend inward scraping tangentially in a spiral around the exterior of the log which is fed through the center of the collar. Typical such cutters are shown in U.S. Pat. No. 4,231,406 to Jonsson and U.S. Pat. No. 4,709,737 to Jonsson.
A more commonly used form of debarker is the so-called rosser-head debarker in which a log is spun while a rotating cylindrical cutter head passes along and rotates against the log, parallel to the axis of the log. As the log is rotated against the head various forms of cutters upon the rosser-head are depended upon to tangentially shear the bark from the log. Typical such prior constructure shown in the Salem rosser-head debarker and the debarkers manufactured by Fulghum Industries and HMC Corp.
Rosser-head debarkers are all characterized in comprising a substantially strong metal cylinder affixed to a powered rotating axis which is parallel to the longitudinal axis of a log to be debarked with periodically extending cutter teeth on the cylindrical outer surface of the debarker head. The impacts upon these cutter teeth are such that they require frequent resetting or replacement and it is difficult to get even two to three months use from a typical debarker head in full industrial usage.
The rosser-head debarkers have difficulty in efficiently debarking species of wood that have fibrous bark such as basswood. The fibers in the bark do not always get cut by the debarker head and can become tangled and cause the operation to be discontinued until the tangles of fiber can be removed. This makes the process of debarking these types of log very costly and inefficient.
One prior attempt was made to construct a bit that could cut wood fiber while debarking. The bit included wings welded unto each side of the bit and then a built-up alloy edge protruded above the top of the bit. There were two major problems with this bit. First, the protrusions became dull within hours of use and eventually wore down completely within a day or two. There was no way to replace the wings because they were welded to the bits. Even if there was a way to replace the wings the fact that they dulled so quickly would mean that the debarker head would need to be serviced every few hours.